1. Field of the Invention
The present invention relates to an information receiving method for receiving, for example, a road traffic information multiplexed over a radio broadcast wave and then making the received traffic information to be displayed together with a road map or the like, a navigation apparatus to which the information receiving method is applied, and a motorcar in which this navigation apparatus is installed.
2. Background of the Invention
Various navigation apparatus which are to be mounted on a motorcar and the like have been developed. The navigation apparatus comprises a data storing means of large capacity such as a CD ROM or the like in which, for example, a road map data is stored, a detector means for detecting a current location, and a display device for displaying the road map in the vicinity of the detected current location on the basis of the data read out of the data storing means. In this case, for the detector means of the current location, there are what uses a positioning system utilizing an artificial satellite for positioning, which is called a GPS (Global Positioning System) (hereinafter merely referred to as a GPS), what uses an autonomous navigation for tracking a change of the current location from a starting point on the basis of information on the direction and the speed of a vehicle, and so forth.
Such data of the road map in the vicinity of the current location detected by the detector means of the current location is read out of a data storing means of large capacity such as the CD ROM or the like and an image signal for displaying the road map is then produced. This image signal is supplied to a display device for displaying the road map in the vicinity of the current location.
In the meantime, there is such a navigation apparatus that displays not only the road map, etc. but also receives a traffic information such as a congested road information or the like and displays the received traffic information on the road map etc. In this case, concerning the reception method of the traffic information, when a system termed e. g. a VICS (Vehicle Information and Communication System) is utilized, there are two ways in one of which the traffic information is obtained by receiving a data broadcast transmitted from a broadcasting station multiplexed over an FM broadcast (radio broadcast) and in the other of which the traffic information is obtained by receiving an infrared-ray signal or an electric wave transmitted from a beacon installed in the vicinity of a road when passing the vicinity of the beacon.
By receiving such traffic information through the navigation apparatus and performing a corresponding display or the like, information such as congested road information which varies every moment, a traffic regulation and so on can be received in a moving car, thus causing the car to be guided. For example, it is possible for a driver to estimate an appropriate route to avoid the traffic jam, based on the displayed information. In case of the navigation apparatus which is capable of establishing a route to a destination, it is also possible to determine automatically the route avoiding the traffic jam based on the received information and to guide the car.
In the meantime, when receiving the traffic information multiplexed over the broadcast wave in the above VICS system and the like, it is necessary to appropriately select a channel (frequency) over which the traffic information is multiplexed and then receive the same. For example, in a system which is now practiced in Japan, frequencies of broadcast wave by which the traffic informations of the administrative districts are transmitted are predetermined in the respective administrative districts, so that it is necessary to set the receiving frequency to a frequency at which the traffic information of the current location (the administrative district) is receivable through user's operation or the like.
In addition, if a motorcar on which the navigation apparatus is mounted moves to change its location (e. g. if it enters another administrative district), it is necessary to change the receiving frequency for receiving the traffic information.
In this regard, when receiving the traffic information multiplexed over a conventional broadcast wave, information of an adjacent broadcasting station contained in the information multiplexed over the broadcast wave is utilized for processing to change the receiving frequency. In other words, when the traffic information or the like is multiplexed over the broadcast wave, information concerning a transmitting frequency of an adjacent broadcasting station in the same network is contained as the multiplexed information. Thus, if a received condition of the broadcast wave which is now under reception becomes worse, an attempt to receive the adjacent broadcasting station indicated by the adjacent broadcasting station information is made. Then, if a better reception than that of the broadcasting station which is now being received can be obtained, a processing to change over to the reception of the adjacent broadcasting station will be performed.
However, if it is arranged in this manner to search the station which can be received better based on the information of adjacent broadcasting station and then change over to receive that station, the station which gives the traffic information of the vicinity of the present moving location will not necessarily be received. This raises a problem. Particularly, even if the broadcasting station which transmits the multiplexed traffic information exists at a unit of the administrative district, there are many cases where in a district in the proximity of a prefectual border, etc. the broadcasting station of an adjacent prefecture can be turned better than that of a prefecture to which the current location pertains. Therefore, if the receiving frequency is changed over relying upon only information transmitted from the adjacent broadcasting station, there will occur such a case where the traffic information concerning the road in question where the car is moving cannot be acquired, but the traffic information of some other district (prefecture) is wrongly received.
Accordingly, there has been the problem in which, if it is arranged to receive the traffic information, etc. by the automatic frequency setting, then the traffic information of the different district from the moving location at that time may be received, so that the required information of the district concerned will not necessary be acquired.
Further, while the case of receiving the traffic information has been described here, the information transmitted in the multiplexed manner over the broadcast wave such as an FM broadcast or the like contains other informations. For example, information of weather forecast, news and so on are also transmitted. When receiving also such information, if a district indicated by the information (e. g. a district corresponding to the weather forecast) does not coincide with the current location, the received information will make no sense, which raises a problem.